8 Tips for Growing AutoFlowering Weed Plants


Plant your autos within the correct time window.


In the northern hemisphere, the summer solstice arrives around June 21 with 16 to 22 hours of light (18 hours in the northwest of France, for example). That’s the point of maximum hours of sunlight per day, and at a better angle (i.e., more vertical) for full plant exposure.

In many areas, spring provides the right temperature to plant autos outdoors (a minimum of 58°F) at the end of May or beginning of June. If you plant (or transplant) them too early outdoors, they tend to produce small, premature harvests, especially since flowering will be accelerated by nights that are too cold. Below 45°F, you’ll encounter exaggerated stretching and stunted bud development.

Given the usual flowering time for autos (most begin to flower at two to three weeks), it’s wise to start them from mid-May to around June 10. This way, your plants get as much sunlight as possible each day, and their “flip” to flowering will occur as the length of days starts to diminish—a strong encouragement for them to start flowering vigorously.

Give your plants a healthy start.

You’ll need to be especially careful during germination. Soak your seeds in a glass of purified water with a pH between 5.5 and 6.0, and stick around to notice how fast they fall to the bottom of the glass. Some will even sprout in less than five hours but it can take considerably more time! A glass of tap water will do fine unless you live in Spain or areas with highly polluted water. Always leave tap water out for 24 hours to allow the chlorine to evaporate. The best sprouting temperature is at 25 – 27 degrees celsious.

Poke the seeds with your finger to push them under the water’s surface, and don’t let them soak longer than 12 to 24 hours. When you notice the first white germ sprouting, you can do one of two things. The easiest is to plant the seed directly into its final pot, which should be filled with a good soil mix available at your local grow shop. My preferences is a mix of 30% cat litter 10% used tea bags and the rest flower soil. Keep the soil moist but not soaked.

Your second option is to put the popped seeds between two unbleached paper towels between two plates and keep them moderately moist. No water should drip from the paper towels; nor should they ever dry out. After a day or two, when you see that the seeds have cracked open and have a tiny root peeking out, carefully transfer them into Jiffy pots for the first 10 days of growth. Be shure to ad 5% peroxyde to water when sprouting, to prevent mold.

Provide your plants with the proper environmental conditions.

It’s important to always dial in the humidity level. Keep it near 80% during the seedling stage, then switch to between 55% and 70% toward the end of the vegetative stage (15 to 25 days from sprouting). In the absence of expensive humidifying equipment, place a dome (such as you’d use for cuttings) over each plant. This is a cheap, easy and very effective method during the early stages of growth. A clear plastic bottle works perfectly for the first week or so, and you can use it indoors, outdoors or in a greenhouse. A simple ceramic ultrasonic system can solve humidity issues in a small to medium-sized area under six by six feet. In a greenhouse, you can set a pipe with nozzles to mist water in the growing area and get a 5°F to 10°F cooling of temperature. The misting system should be coupled with a controller that manages ventilation, temperature and humidity.

Use the best growing medium possible.


No reason to cut corners here! Your harvest is directly linked to the quality of your genetics, grow medium, nutrients and environmental conditions. Remember, over watering and overfeeding are the most common mistakes that a beginner can make.

Your medium needs to have the airiest structure possible, so anything you can add to improve aeration and water retention is a good thing: coco coir, clay pellets, perlite, vermiculite, etc. Here in Europe, we use Plagron, Canna and Biobizz, but in North America people seem to prefer Pro-Mix, FoxFarm and Sunshine Mix. Whichever option you choose, be sure it’s light, airy and has a pH range of 6.0 to 6.5. Your auto-flowering roots will grow as though they’re in a hydroponic system.

Don’t over-water!

One of the worse things that can happen to a plant is too much water: The roots become suffocated and are unable to carry nutrients to the plant. An over-watered plant will show stunted growth, and beginners can sometimes misdiagnose this as a nutrient problem, causing them to compound the situation by adding nutrients—and more water—to an already suffocating plant and quite literally drowning it.

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A good solution is to weigh your plants with their pots dry (after repotting, for example), add 5% or 10% to that weight, and use that number as a reference for when you need to water. Some manufacturers suggest watering plants with 20% of the volume of their containers. For example, a plant in a 3-gallon pot needs about a half-gallon of nutrient solution for every watering.

It’s important that your roots have a period of relative dryness before they’re watered again. If you’re watering an outdoor guerrilla grow of auto-flowering plants, I suggest adding a drop of unscented dish soap per liter of water or nutrient solution. This aids in absorption and keeps the liquid from pooling at the top of your grow site.

Feed your plants lightly.

Use organic nutrients (it’s harder to overfeed with natural ingredients), and remember that auto-flowering plants prefer light feeding in comparison to their photoperiod-determined counterparts. I’ve experienced issues a number of times with over-fertilized plants, but the most severe cases were always with the autos.

Given their smaller and more fragile root structure, auto-flowering plants can handle only half the usual feeding regimen of regular plants, which develop larger root systems. In a well-aerated “living organics” medium (one that contains beneficial bacteria and compost with humic and fulvic acids), your short-lived autos shouldn’t need much feeding anyway.

Some boosters can be added to enhance root production, and many of these are available in grow shops. Here in Europe, many growers prefer House & Garden Roots Excelurator. If you have the space, a compost-brew juice aerated for 24 hours will give your plants a good boost.

Pinch and prune early, if at all.

Regular plants should only be pinched and pruned during their vegetative stage, and this rule applies to auto-flowering plants as well. Because the window in which to bulk up your autos is small, choose when to employ these techniques wisely. If your strains start their flowering stage super-early or didn’t get a strong start to life, you should avoid pinching and pruning altogether.

For plants that have a longer flowering time, it is possible to pinch or prune—or, even better, to use a less traumatic technique such as LST (low-stress training) early on. Use fishing weights to weigh down the branches and expose the lower areas of the plant to light. You can also bend the branches carefully to get them more horizontal. Always remember that auto-flowering plants have a brief lifespan and won’t recover well from stressful situations. It’s wise to experiment with pruning regular plants before trying it on your auto-flowering ones.

Harvest sequentially over time.


With all marijuana plants, the main tops are harvestable before the lower parts of the plant. If possible, wait six to 10 days between your first harvest of the main or top colas and the rest of the plant. This will result in added weight, stronger effects and better quality overall.

As they approach harvest, your plants must be closely monitored. Pay attention to the trichomes and take into account that wind, cold and heat can affect them outdoors. Exercise patience—a good rule of thumb is to give autos a week more of flowering outdoors than in, and don’t rely solely on the breeder’s recommendations for flowering times. For example, an early spring grow will slightly lengthen the plant’s maturation schedule because the hours of sunlight are still increasing, and the plants feel it. If you plant them after the summer solstice, you will notice a shorter flowering time by a week or two.

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